Stripped screw for caliper

I own a Giant 2013 XTC Composite 29er 3 with the avid elixir 1 disc brakes. I removed the caliper so I can readjust the braking because it was squealing like crazy so i figured that was the case. I'm not sure what they used to screw it in at the shop, but man was it hard to unscrew it from the frame. I saw some "powder" coming out of the screw holes. Anyhow, I screwed the caliper back to the frame and noticed it stripping. So I'd like to get my hands on some new screws before it gets worse and I'm stuck. By the way, the "powder" coming from the frame doesn't indicate me stripping it so I won't be able to screw another caliper to the frame?

Oh so basically the threading that's into my frame didn't strip pretty much? It's only a compound to tighten the screw and lock it into place? Bare with me... I'm new to disc brakes haha. What's stripped is the screw itself that screws the rear caliper to my frame.

I also did notice when I start squeezing the front brakes, the forks shake... is this normal? When the bike is stationary and when both brakes are locked... the neck of the bike doesn't move at all. So is it normal? I'm so new to this haha...

If you do a search in the Brake section you will see plenty on Avid hydros. It's new, so take your bike into the giant dealer and let a tech look at it, show you some tricks and give you a replacement bolt if necessary. You can use the other bolt to check threading by hand until you go in. Think SLX as a replacement.